Colored metal clay and colored metals

ABSTRACT

A composition for forming metal objects includes (a) first particles containing a jewelry-metal, and (b) second particles containing a refractory metal oxide. The composition allows the preparation of jewelry-metal in a large variety of colors.

BACKGROUND

[0001] The present invention relates to metal clays with refractory stains.

[0002] Upon sintering, jewelry-metal clays form pure or almost pure jewelry-metal objects that retain the basic shape of the jewelry-metal clay. The clays contain a jewelry-metal powder and a binder; the binder is mostly removed during the sintering process. Jewelry-metal clays are described in U.S. Pat. Nos. 5,376,328 and 5,328,775. Jewelry-metal clay is referred to in the trade as precious metal clay, or PMC, and is available from RIO GRANDE, 7500 Bluewater Road N.W., Albuquerque, N. Mex., 87121, among others.

[0003] The ability to color jewelry-metal objects is limited. Jewelry-metal gold is an excellent example. Although white, rose, green, and varying shades of yellow gold are known, each is made by alloying pure gold with a second metal. The achievable color variation in any jewelry-metal, whether 24 karat gold, 18 karat gold, 14 karat gold, 10 karat gold, Nu-gold (88% wt. Cu/12% wt. Zn), fine silver, sterling silver (92.5% wt. Ag/7.5% wt. Cu), nickel silver (65% wt. Cu/18% wt. Ni/17% wt. Zn), platinum, palladium, ruthenium, rhodium, aluminum, brass, lead, nickel, iridium, indium, copper, zinc, or combinations thereof, is typically limited to the alloys these metals form. Accordingly, there is a need to expand the varieties of colors of jewelry-metal articles.

[0004] Refractory stains have many uses and are widely used to color ceramics. Prior to firing, the stain is incorporated into the slip and/or applied as a glaze. The stains are prepared by mixing together metal oxides and various inorganic and metal binders, which are fired for color stability, and then ground.

BRIEF SUMMARY

[0005] In a first aspect, the present invention includes a composition for forming metal objects, including first particles containing a jewelry-metal, and second particles including a refractory metal oxide. The composition may be made by mixing these ingredients together.

[0006] In a second aspect, the present invention includes a metal object, containing a jewelry-metal; and second particles containing a refractory metal oxide, in the jewelry-metal.

DETAILED DESCRIPTION

[0007] Jewelry-metal clays and refractory stains may be combined to form a colored metal clay. When sintered, the colored metal clay forms a colored jewelry-metal article, due to incorporation of the stain. Because jewelry-metal clays are sintered to remove their binder constituents at temperatures lower than those at which refractory stains degrade, jewelry-metals having the color of the stain are possible. The stain is present on the surface and in the subsurface of the finished jewelry-metal article, not simply as a surface coating. The actual color of the final product will be influenced by the natural color of the jewelry-metal and the color of the stain.

[0008] Jewelry-metal clays form almost pure jewelry-metal articles after sintering, preferably at temperatures of from 1470° F. to 1830° F. Because refractory stains do not undergo significant chemical reaction and degradation during sintering at these, and higher, temperatures, the stains may be incorporated into the jewelry-metal clays. In the case of jewelry-metals which cannot tolerate sintering in air without significant oxidation, sintering may be carried out under vacuum, under an inert atmosphere, such as argon or nitrogen, or under a reducing atmosphere, such as hydrogen or methane.

[0009] Although the coloring of jewelry-metal objects is preferably achieved by mixing a refractory stain into a jewelry-metal clay before sintering, clays are not required. A jewelry-metal may be colored with stain, for example, by mixing the powdered metal and stain together, and then sintering the mixture below the melting point of the metal. Furthermore, once formed by any method, colored jewelry-metal may be mechanically formed into the desired shape using hand-tools, machines, or dies. Colored jewelry-metal wires could be produced in this manner.

[0010] As described in U.S. Pat. Nos. 5,328,775 and 5,376,328, a pure or almost pure jewelry-metal object may be formed as the solid-phase sintered product of a jewelry-metal clay. To manufacture the jewelry-metal article, a moldable clay mixture, containing a jewelry-metal powder and a binder, is shaped into a molded object. The molded object is then sintered An almost pure jewelry-metal article results which retains the shape of the clay, typically with some shrinkage. To prevent the metal from melting and loosing the shape into which the clay was molded, the clay is sintered at a lower temperature than the melting point of the jewelry-metal. Sintering is defined as heating sufficiently to cause the metal particles to stick together, but below the melting point of the metal.

[0011] Moldable clay mixtures are produced by blending jewelry-metal powders with a binder. Preferably, the binder is a cellulose binder prepared by blending a cellulose with water. Addition of a surface-active agent during mixing of the jewelry-metal powder and binder allows for more uniform mixing in a short time period. Addition of an adhesion-preventing agent, such as di-n-butyl phthalate or an oil such as a vegetable oil, prevents the clay from sticking to the skin of the hand during molding.

[0012] A preferable moldable clay mixture contains 50 to 90% by weight of jewelry-metal powder with an average particle diameter of at most 1000 μm, preferably at most 600 μm, most preferably at most 200 μm; 0.8 to 8% by weight of binder, more preferably a water-soluble cellulose binder; 0.08 to 3% by weight of a surface-active agent; and 0.1 to 4% by weight of oil; with the balance water and unavoidable impurities. Sintering of this jewelry-metal clay results in a solid-phase sintered product of a jewelry-metal.

[0013] Currently, three jewelry-metal clays are available from RIO GRANDE. An 80% pure silver clay (STANDARD SILVER PMC) is available with a recommended sintering time of two hours at 1650° F. A 90% pure silver clay (SILVER PMC+) is available with a recommended sintering time of thirty minutes at 1470° F. This clay provides the benefits of less shrinkage, lower sintering temp, and less sintering time. A 24 karat yellow gold clay (STANDARD GOLD PMC) is also available with a recommended sintering time of two hours at 1830° F. Other jewelry-metal clays may be prepared by mixing powder of one or more metals or alloys with a binder, optionally a solvent which will evaporate or burn away (water, ethanol, isopropanol, methanol, acetone, etc.), optionally a surface-active agent, and optionally an adhesion-preventing agent (di-n-butyl phthalate, vegetable oil, etc.).

[0014] Jewelry-metal clays may also be formed by more conventional methods involving the combination of jewelry-metal powders and binders such as bentonite, clay, glue, and boiled rice or wheat flower, and optionally water, as described in Japanese Patent Applications laid open with Publication Numbers 59-143001 and 63-403. Unlike cellulose-binder clays, these binders may remain in the jewelry-metal article after drying or sintering.

[0015] Refractory stains have been used to color ceramic articles for over 100 years and are available in numerous colors. In addition to shades of pink, blue, black, white, crimson, coral, purple, orange, gray, green, brown, yellow, and red, many color shades are available. Refractory stains may be obtained as MASON STAINS, available from MASON COLOR WORKS, INC., East Second Street, P.O. Box 76, East Liverpool, Ohio, 43920, or as WALKER STAINS, available from WALKER CERAMICS, 55 Lusher Road, Croydon, Australia, 3136.

[0016] Refractory stains are metal oxides which are fired for color stability to form refractory metal oxides and ground into a fine powder with an average particle diameter of at most 50 mesh (for example 254 to 297 microns), preferably at most 100 mesh (for example 122 to 149 microns), and most preferably at most 200 mesh (for example 50 to 74 microns). One or more oxides of metals such as aluminum (Al₂O₃), antimony (Sb₂O₃), boron (B₂O₃), calcium (CaO), chromium (Cr₂O₃), cobalt (CoO), iron (Fe₂O₃), manganese (MnO₂), nickel (NiO), praseodymium (Pr₆O₁₁), selenium (SeO₂), silicon (SiO₂), tin (SnO₂), titanium (TiO₂), vanadium (V₂O₅), zinc (ZnO), and zirconium (ZrO₂) are combined in various proportions and then fired, to attain the desired color. In addition to metal oxides, refractory stains optionally contain various metal and inorganic binders. Any combination may be used, as long as the metal oxide stain can withstand firing at a temperature high enough to allow sintering of the metal clay.

[0017] The stains may be any color, including black, white, or transparent. To achieve greater color variation, mixtures of stains are possible. Some examples of the available stain colors and the metal oxide components combined to form them are provided in the following MASON COLOR charts. MASON COLOR COMPOSITION CHARTS New See No. Greens Al Ca Co Cr Fe Ni Pr Si Sn Ti V Zn Zr Ref. 6200 Evergreen X X X 3, 5 6201 Celadon X X X X X 1, 3, 6, 8 6202 Florentine X X X 1, 3, 6, 8 6204 Victoria Green X X X X 3, 5, 9 6206 Grass Green X X X X 3, 5, 9 6207 Celeste X X X X 1, 3, 6 6209 Chrome Green X X 3, 5 6211 Pea Green X X X X 1, 3, 6, 8 6219 French X X X X X 1, 3, 5, 8 6221 Turquoise X X X X X X 3, 5 6223 Ivy X X X 3, 5 6224 Dk. Green X X X X X 3, 5 6226 Dk. Leaf X X X X X 1, 3, 6, 8 6234 Myrtle Green X X X 1, 3, 6, 8 6236 Chartreuse X X X X 1, 3, 6 6242 Bermuda X X X X 3, 6 6244 Deep Sea X X X X X 1, 3, 6, 8 6246 Blue Green X X X X X 3, 6, 8 6254 Dk. Teal Green X X X X X 1, 3, 6, 8 6255 Jade Green X X X X X 1, 3, 6, 8 6263 Victoria X X X X 3, 5, 9 6264 Victoria X X X X 3, 5, 9 6265 Leaf Green X X X X X X 3, 5, 9 6266 Peacock X X 1, 3, 6, 8 6267 Emerald X X X X X 3, 5, 9 6268 Sea Green X X X X 1, 3, 6, 8 6271 Mint X X X X X X 3, 5, 9 6274 Nickel Silicate X X 1, 3 6280 Avocado X X X X X X X X X 3, 6 6288 Turquoise X X X X X 3, 5, 9 6296 Dk. Spruce X X X X 1, 3, 6, 8 New See No. Blacks Co Cr Fe Mn Ni Sn Zn Ref. 6600 Best Black X X X X 1, 3, 6 6601 Velvet Black X X X X X 1, 3, 6 6609 Black X X X X X X 1, 3, 6 6612 Onyx Black X X X X 1, 3, 6 6616 Chrome-Free X X X 1, 3, 6 6650 Cobalt-Free X X 3, 5 6657 Black X X X 3, 5 6666 Cobalt-Free X X X 3, 5 New See No. Blues Al Co Cr Fe Ni Si Sn V Zn Zr Ref. 6300 Mazerine X X X 1, 3, 6 6302 Cadet X X X X X X 1, 3, 6 6305 Teal X X X X X 1, 3, 6 6306 Vivid Blue X X X X 1, 3, 6 6307 Pastel Blue X X X X 1, 3, 6 6308 Delphinium X X X 1, 3, 6 6310 Wedgwood X X X 1, 3, 6 6313 Medium Blue X X X 1, 3, 6 6315 Zirconium X X X 1, 3, 6 Vanadium 6320 Delft X X X X X 1, 3, 6 6330 Cobalt Aluminate X X 1, 3, 6 6336 Peacock X X X X X X 3, 6 6338 Cobalt Meta- X X 1, 3, 6 Silicate 6339 Royal X X X 1, 3, 6 6343 Mediterranean X X X X X 1, 3, 6 6350 Bright Blue X X X X X X 1, 3, 6 6360 Willow X X X X X 3, 5 6363 Sky Blue X X X 1, 3, 6 6364 Turquoise X X X 1, 3, 6 6368 Copen Blue X X X X 1, 3, 6 6371 Dark Teal X X X 1, 3, 6 6373 Turquoise X X X X X 3, 6 6374 Dk. Turquoise X X X 1, 3, 6 6376 Robin's Egg X X X 1, 3, 6 6378 Zirconium X X X 1, 3, 6 Vanadium 6383 Cobalt Aluminate X X 1, 3, 6 6386 Navy Blue X X X X X X 1, 3, 6 6388 Mazerine X X 1, 3, 6 6389 Sapphire Blue X X 1, 3, 6 6391 Zirconium X X X 1, 3, 6 Vanadium 6393 Turquoise X X X X X X 3, 6 6396 Peacock X X X X X X 1, 3, 6 6398 Deep Peacock X X X 1, 3, 6 New See No. Whites Al B Ca Si Sn Zr Ref. 6700 White X X X 3, 6 6768 Tin White X X X 3, 6 6790 White for Matting X X 3, 6 New Pinks, Crimsons, See No. & Corals Al Ca Cr Fe Mn Si Sn V Zn Zr Ref. 6000 Shell Pink X X 3, 5, 9 6001 Alpine Rose X X 3, 5, 9 6002 Rose Pink X X 3, 5, 9 6003 Crimson X X 3, 5, 9 6004 Crimson X X 3, 5, 9 6005 Deep Crimson X X 3, 5, 9 6006 Deep Crimson X X 3, 5, 9 6007 Peach X X X 3, 5, 9 6008 Peach X X X 3, 5, 9 6009 Coral X X X 3, 5, 9 6020 Manganese X X 1, 3 Alumina 6023 Clover Pink X X X X 3, 5 6029 Persimmon X X X X 3, 8 6031 Deep Salmon X X X 3, 5 6032 Coral X X X 3 6052 Doll Flesh X X X X X 1, 3, 6 6065 Chrome Alumina X X 1, 3, 6 6067 Pink Extender X X X 3, 5 6069 Dark Coral X X X 3 6090 Coral X X X 3, 5, 9 6098 Flesh X X X X 3, 5, 9 New See No. Yellows Al Cr Fe Pr Sb Si Sn Ti V Zn Zr Ref. 6404 Vanadium X X X 1, 3, 6 6405 Naples X X X X 3, 6 6406 Buttercup X X X X 3, 6 6407 Marigold X X X X 3, 6 6408 Praseodymium X X X 3, 6 6433 Praseodymium X X X 3, 6 6440 Vanadium X X 1, 3, 6 6450 Praseodymium X X X 3, 6 6464 Zirconium X X X 1, 3, 6 6471 Old Gold X X X X X X 1, 3, 6 6485 Titanium X X X 1a, 3 New Purples & See No. Lavenders Al Ca Co Cr Fe Mn Ni Si Sn V Zn Zr Ref. 6303 Deep Orchid X X X X 3, 5, 9 6317 Lavender X X X X X 3, 5, 9 6318 Amaethyst X X X X X 3, 5, 9 6319 Lavender X X X X X 1, 3 6324 Violet X X X X X X X 3, 5, 9 6331 Orchid X X X X X 3, 5, 9 6332 Orchid X X X X X 3, 5, 9 6333 Lavender X X X X X 3, 5, 9 6381 Blackberry Wine X X X X X X 3, 5, 9 6385 Pansy Purple X X X X 3, 5, 9 6387 Mulberry X X X X 3, 5, 9 6392 Dusty Lavender X X X X X 3, 5, 9 New Browns & See No. Oranges Al Ca Co Cr Fe Mn Si Sn Ti V Zn Zr Ref. 6100 Woodland X X X X X 3, 6, 7 6101 Chestnut X X X X 3, 6, 7 6103 Golden X X X X 3, 6, 7 6104 Fawn X X X X 3, 6, 7 6107 Dk. Golden X X X X 3, 6, 7 6108 Walnut X X X X 3, 6, 7 6109 Deep Brown X X X X 3, 6, 7 6110 Violet Of Iron X X X 3, 6, 7 6111 Spice Brown X X X 3, 6, 7 6113 Claret X X X 3, 6, 7 6119 Russet X X X X X 3, 6, 7 6121 Saturn X X X X 3, 6, 7 Orange 6122 Cedar X X X X 3, 6, 7 6123 Saddle X X X X 3, 6, 7 6124 Chocolate X X X X X 3, 6, 7 6125 Leather X X X X 3, 6, 7 6126 Hazelnut X X X X 3, 7 6129 Golden X X X X 3, 6, 7 Ambrosia 6131 Titanium Iron X X 1a, 3, 6 3132 Red Brown X X X 3, 6, 7 3133 Sorrel Brown X X X 3, 6, 7 6134 Red Brown X X X 3, 6, 7 6149 Iron Silicate X X 3, 6, 7 6155 Black Brown X X 3, 6, 7 6153 Seal Brown X X X X 3, 6, 7 6160 Dk. Chocolate X X X X X 3, 6, 7 6163 Terra Cotta X X X X 3, 6, 7 6166 Camel Beige X X X X X X 3, 6, 7 6190 Deep Brown X X X 3, 6, 7 6194 Manganese X X 3, 6, 7 Silicate New See No. Greys Al Co Cr Fe Mn Ni Sb Si Sn Ti V Zr Ref. 6500 Sage X X X X 1, 3, 6 6503 Taupe X X X X X 3, 5, 9 6506 Pearl X X X X X 3, 6 6515 Soft X X X X X X 3, 5 Medium 6523 Soft X X X X X X X X X 3, 5 Green 6527 Shadow X X X X X X 3, 5, 9 6528 Charcoal X X X X X 3, 6 6530 Silver X X X X X 3, 6 6531 Slate X X X X X 1, 3, 6 6537 Mouse X X X X X X 3, 5, 9 6540 Blue-Grey X X X X X 3, 6 6572 Neutral X X X 3, 5 6573 Rose X X X X X X 3, 5, 9 Taupe 6584 Tin Grey X X 2, 8 6591 Gun Metal X X X 3, 6

[0018] Reference Notes for Color Composition Charts

[0019] 1. Can be used as a ‘body stain’ in porcelain at high temperatures. All of the brown colors can be used as ‘body stains’ but will vary in shade considerably depending on the composition of the body and temperature at which it is fired.

[0020] 1a. Use only as ‘body stain’

[0021] Firing Temperatures can only be a rough guide. Firing at 2200° F. on a slow schedule may give the equivalent maturing as firing at 2300° F. on a fast schedule. The cycle, atmosphere, and rate of cooling will affect the color.

[0022] 2. Max. firing limit 2156° F. (1180° C.).

[0023] 3. Max. firing limit 2300° F. (1260° C.)

[0024] 4. Max. firing limit 1976° F. (1080° C).

[0025] Zinc Oxide influences the color in a glaze more than any other element. Generally, zincless glazes should not contain magnesium oxide. Some colors containing zinc are to be used in a zincless glaze. The zinc in the color is in a combined form and will not harm the color, but free zinc oxide in the glaze can destroy the color.

[0026] 5. Do not use zinc in glaze.

[0027] 6. May be used with zinc or without zinc.

[0028] 7. Zinc not necessary, but gives better results

[0029] 8. Best results with no zinc.

[0030] Calcium Oxide content as calcium carbonate should be from 12-15% for best color development. Adding the molecular equivalent of calcium oxide with wollastonite, a natural calcium silicate, often gives better uniformity. The increased silica from the wollastonite must be subtracted or the glaze will have a poor surface.

[0031] 9. Glaze must contain from 6.7 to 8.4% CaO (12-15% CaCO₃)

[0032] Metal to Metal Oxide Conversion Key for Color Composition Charts Al Aluminum Oxide Al₂O₃ B Boric Oxide B₂O₃ Ca Calcium Oxide CaO Co Cobalt Oxide CoO Cr Chromium Oxide Cr₂O₃ Fe Iron Oxide Fe₂O₃ Mn Manganese Dioxide MnO₂ Ni Nickel Oxide NiO Pr Praseodymium Oxide Pr₆O₁₁ Sb Antimony Oxide Sb₂O₃ Si Silicon Dioxide SiO₂ Sn Tin Dioxide SnO₂ Ti Titanium Dioxide TiO₂ V Vanadium Pentoxide V₂O₅ Zn Zinc Oxide ZnO Zr Zirconium Dioxide ZrO₂

[0033] Refractory metal oxides are metal oxides stable in air at a temperature of at least 1600° F., preferably at least 1800° F., more preferably at least 1976° F, most preferably at least 2700° F. Here, the term “refractory” means stable in air at temperatures of at least 1600° F., and “stable” means without significant color degradation after heating in air to the specified temperature and cooling to room temperature.

[0034] Mesh is a way to define the diameter of a particle by the size of interstitial site in a wire mesh through which the particle will pass. For example, 200 mesh particles will pass through the interstices of a wire screen with 200 wires per inch. Since the particle size that will pass through a screen decreases with increasing mesh number, particles defined as 200 mesh will contain all those capable of passing through a 200 wire per inch screen and smaller. Two-hundred mesh particles contain 400 mesh, but not 100 mesh.

[0035] Since mesh is not a direct measurement of individual particles, but a characteristic of those that can pass through a specific screen, it is best thought of as representing the average particle diameter of all the particles that pass through the screen, averaged. Fifty mesh particles preferably have an average particle diameter of from 254 to 297 microns. One-hundred mesh particles preferably have an average particle diameter of 122 to 149 microns. Two-hundred mesh particles preferably have an average particle diameter of 40 to 85 microns, more preferably 45 to 80 microns, and most preferably 50 to 74 microns. Four-hundred mesh particles have an average particle diameter of 5 to 47 microns, preferably 10 to 42 microns, and most preferably 15 to 37 microns.

EXAMPLES Example 1

[0036] Five grams of silver jewelry-metal clay was weighed and handled in accordance to information provided by MITSUBISHI MATERIALS CORPORATION. After shaping three separate five gram clay samples into pancake-like forms, 0.1 gram of refractory stain was added to the first, 0.3 gram to the second, and 0.5 gram to the third. Each sample was kneaded until the refractory stain was thoroughly distributed throughout the jewelry-metal clay. A droplet of water was added to ease kneading of the 0.3 and 0.5 gram stain addition samples.

[0037] The jewelry-metal clay samples containing the refractory stain were each rolled into an oval sheet and weighed. The samples were allowed to thoroughly dry before firing, and their dry weights recorded.

[0038] The samples were fired on an earthenware tile, dusted with clean alumina hydrate. The tile was stilted and placed in an electronically monitored electric kiln. The samples were fast-fired according to MITSUBISHI MATERIALS CORPORATION's specifications (1650° F. for two hours). The kiln was allowed to cool before the samples were removed. The fired samples were weighed and the weights recorded.

[0039] The samples were successfully colored with the color of the chosen refractory stain. The color was perfectly distributed. The sample containing the highest concentration (0.5 gram or 10% by weight) of refractory stain provided a darker colored silver article. The sample containing the lowest concentration (0.1 gram or 2% by weight) of refractory stain provided a lightly colored silver article. The resultant articles were malleable, like uncolored jewelry-metal clay sintered articles. The resultant articles demonstrated shrinkage, like uncolored jewelry-metal clay sintered articles, but showed no additional deformation or loss of detail in comparison to uncolored articles.

Prophetic Example 1

[0040] Five grams of gold jewelry-metal clay is weighed and handled in accordance to information provided by MITSUBISHI MATERIALS CORPORATION. After shaping three separate five gram clay samples into pancake-like forms, 0.1 gram of refractory stain is added to the first, 0.3 gram to the second, and 0.5 gram to the third. Each sample is kneaded until the refractory stain is thoroughly distributed throughout the jewelry-metal clay. A droplet of water is added to ease kneading of the 0.3 and 0.5 gram stain addition samples.

[0041] The jewelry-metal clay samples containing the refractory stain are each rolled into an oval sheet and weighed. The samples are allowed to thoroughly dry before firing, and their dry weights recorded.

[0042] The samples are fired on an earthenware tile, dusted with clean alumina hydrate. The tile is stilted and placed in an electronically monitored electric kiln. The samples are fast-fired according to MITSUBISHI MATERIALS Corporation's specifications (1830° F. for two hours). The kiln is allowed to cool before the samples are removed. The fired samples are weighed and the weights recorded.

Prophetic Example 2

[0043] A five gram sample of finely ground silver is weighed. One-half gram of refractory stain is added and thoroughly mixed with the silver powder. The powdered mixture of silver and refractory stain is pressed into a cylinder and fired in an electronically monitored electric kiln at 1470° F. for thirty minutes. The kiln is allowed to cool before the sample is removed. The colored silver mass is then removed and could be shaped into the desired item with hand tools, machine, or die. The colored silver could also be hammered or drawn into wires.

[0044] Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

1. A composition for forming metal objects, comprising: (a) first particles comprising a jewelry-metal, and (b) second particles comprising a refractory metal oxide.
 2. The composition of claim 1, wherein said jewelry-metal is selected from the group consisting of silver, gold, and platinum.
 3. The composition of claim 2, wherein said first particles consist essentially of a member selected from the group consisting of fine silver, sterling silver, 24 karat gold, 18 karat gold, 14 karat gold, and 10 karat gold.
 4. The composition of claim 2, further comprising (c) a binder.
 5. The composition of claim 2, further comprising (d) a solvent.
 6. The composition of claim 2, further comprising (e) a surface-active agent.
 7. The composition of claim 2, further comprising (f) an adhesion-preventing agent.
 8. The composition of claim 2, further comprising (g) third particles comprising another refractory metal oxide.
 9. The composition of claim 2, wherein said first particles have an average particle diameter of at most 1000 μm, and said second particles have an average particle diameter of at most 300 μm.
 10. The composition of claim 4, further comprising a solvent, and wherein said refractory metal oxide is stable in air at a temperature of at least 1976° F.
 11. The composition of claim 10, wherein said solvent is water, and said binder is a cellulose binder.
 12. A method of making the composition of claim 1, comprising mixing together ingredients, said ingredients comprising (a) said first particles, and (b) said second particles.
 13. The method of claim 12, wherein said ingredients further comprise (c) a binder and (d) a solvent.
 14. A method of making the composition of claim 10, comprising: mixing together ingredients, said ingredients comprising (a) said first particles, (b) said second particles, (c) said binder and (d) said solvent.
 15. A metal object, comprising: (a) a jewelry-metal, and (b) second particles comprising a refractory metal oxide, in said jewelry-metal.
 16. The metal object of claim 15, wherein said second particles are in a subsurface of said metal object.
 17. The metal object of claim 16, wherein said second particles are present throughout said metal object.
 18. The metal object of claim 15, wherein said jewelry-metal is selected from the group consisting of silver, gold, and platinum.
 19. The metal object of claim 18, wherein said jewelry-metal comprises at least one metal selected from the group consisting of fine silver, sterling silver, 24 karat gold, 18 karat gold, 14 karat gold, and 10 karat gold.
 20. The metal object of claim 15, further comprising (g) third particles comprising another refractory metal oxide.
 21. The metal object of claim 15, wherein said second particles have an average particle diameter of at most 300 μm.
 22. The metal object of claim 15, wherein said refractory metal oxide is stable in air at a temperature of at least 1976° F.
 23. A method of making a metal object, comprising: sintering the composition of claim
 1. 24. A method of making a metal object, comprising: sintering the composition of claim
 2. 25. A method of making a metal object, comprising: sintering the composition of claim
 3. 26. A method of making a metal object, comprising: sintering the composition of claim
 9. 27. A method of making a metal object, comprising: sintering the composition of claim
 10. 28. A method of making a metal object, comprising: sintering the composition of claim
 11. 29. The method of claim 23, wherein said sintering is at a temperature of at least 1470° F.
 30. The method of claim 27, wherein said sintering is at a temperature of at least 1470° F. 